On Thu, Feb 27, 2020 at 11:12 AM <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> The patch below does not apply to the 5.4-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
Thanks, I'll send the backport for 5.4-stable tree.
Stefano
>
> thanks,
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
> From 7143b5ac5750f404ff3a594b34fdf3fc2f99f828 Mon Sep 17 00:00:00 2001
> From: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> Date: Fri, 21 Feb 2020 16:42:16 +0100
> Subject: [PATCH] io_uring: prevent sq_thread from spinning when it should stop
>
> This patch drops 'cur_mm' before calling cond_resched(), to prevent
> the sq_thread from spinning even when the user process is finished.
>
> Before this patch, if the user process ended without closing the
> io_uring fd, the sq_thread continues to spin until the
> 'sq_thread_idle' timeout ends.
>
> In the worst case where the 'sq_thread_idle' parameter is bigger than
> INT_MAX, the sq_thread will spin forever.
>
> Fixes: 6c271ce2f1d5 ("io_uring: add submission polling")
> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 6e249aa97ba3..b43467b3a8dc 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -5142,6 +5142,18 @@ static int io_sq_thread(void *data)
> * to enter the kernel to reap and flush events.
> */
> if (!to_submit || ret == -EBUSY) {
> + /*
> + * Drop cur_mm before scheduling, we can't hold it for
> + * long periods (or over schedule()). Do this before
> + * adding ourselves to the waitqueue, as the unuse/drop
> + * may sleep.
> + */
> + if (cur_mm) {
> + unuse_mm(cur_mm);
> + mmput(cur_mm);
> + cur_mm = NULL;
> + }
> +
> /*
> * We're polling. If we're within the defined idle
> * period, then let us spin without work before going
> @@ -5156,18 +5168,6 @@ static int io_sq_thread(void *data)
> continue;
> }
>
> - /*
> - * Drop cur_mm before scheduling, we can't hold it for
> - * long periods (or over schedule()). Do this before
> - * adding ourselves to the waitqueue, as the unuse/drop
> - * may sleep.
> - */
> - if (cur_mm) {
> - unuse_mm(cur_mm);
> - mmput(cur_mm);
> - cur_mm = NULL;
> - }
> -
> prepare_to_wait(&ctx->sqo_wait, &wait,
> TASK_INTERRUPTIBLE);
>
>
--
Stefano Garzarella
Software Engineer, Virt Team
Red Hat
